Nonadherent use of smoking cessation medications is very common and highly associated with failure to quit smoking. However, little is presently known about how to affect adherence, or whether greater adherence will actually improve cessation success (i.e., its causal role is unknown). Project 3 is designed to address three chief aims: (1) to identify the factors that influence adherence to smoking cessation medication; (2) to determine the association between medication adherence and smoking cessation, and (3) to develop new, cost-effective adherence interventions that are feasible for use in real-world healthcare settings and that improve both medication adherence and smoking cessation outcomes. These research goals will be addressed via two experiments conducted in real-world primary care settings that will assess several types of promising adherence interventions designed to boost both adherence rates and cessation success. These interventions include a cognitive intervention designed to modify smokers' incorrect beliefs about medication and cessation, interventions that provide feedback and problem solving counseling based upon real-time recording of medication use, and a contingency management intervention that reinforces adherence behavior. Strengths of this research are that it will: use smokers recruited in primary care settings; reveal the relative, additive, and interactive effects of these adherence interventions; use multiple, convergent measures to achieve an accurate assessment of adherence; and use mediational analyses to reveal the extent to which adherence change translates into higher abstinence rates. Finally, this research will identify an optimal set of adherence interventions for use in real-world settings. Such interventions might be used for a broad range of health conditions where medication adherence is a problem.